1. Field of the Invention
The present invention relates to a synchronizing control system for a plurality of controllers.
2. Description of the Related Art
In a controller such as a numerical controller or a robot controller, the motor control is implemented in accordance with timing signals of a fixed cycle generated by the hardware of the controller, that is to say, by an interpolation cycle (ITP signal). A main CPU of the controller delivers the motion amount of each ITP signal interval to a DSP (digital signal processor) that controls a servomotor. The DSP distributes the command motion amount to each control cycle (position, speed control cycles) obtained by further subdividing of the ITP signal interval to control the position and speed of the motor.
On the other hand, a system in which a controller such as a numerical controller or robot controller is connected in plurality and a plurality of controllers are synchronously operated is also known.
In this system, a timing signal from a controller serving as a master unit is transmitted to controllers of slave units by way of a bus or a network, and motors to be driven and controlled by the controllers are synchronously operated as a result of the synchronous operation of the plurality of controllers in accordance with this timing signal.
While timing signal lag occurs in controllers of this type due to transmission delays and so on, a technique for correcting this lag to generate signals of the same timing has been disclosed (Japanese Patent Application Laid-Open No. 4-125210).
In addition, a moving body communication system in which, in the data transmission between a base station apparatus and a base station controller, the predicted arrival time of a data frame sent from the base station controller is estimated by the base station apparatus and this predicted arrival time is notified to the base station controller and, at the base station controller, the transmission timing of the data frame is sped up in accordance with this notified predicted arrival time has also been disclosed (see Japanese Patent Application Laid-Open No. 2001-358793).
As a synchronization system for a plurality of controllers such as numerical controllers or robot controllers connected by a bus or network, a patent application proposing a method for correcting timing signal synchronization lag in which the controller serving as a slave unit itself comprises timing signal generation means, and the master unit and slave unit are synchronized as a result of correction of the phase difference between a timing signal sent from the controller of the master unit and a timing signal generated by the slave unit itself has also been submitted in Japan (Japanese Patent Application Serial No. 2005-60863; disclosed as Japanese Patent Application Laid-Open No. 2006-244264 on Sep. 14, 2006).
In the invention described in Japanese Patent Application Laid-Open No. 2006-244264, the phase difference between the timing signal sent from the controller of the master unit and the timing signal generated by the slave units itself is determined, and the timing signal generated by the slave units itself is corrected so that the phase difference thereof is “0”.
However, in the invention described in Japanese Patent Application Laid-Open No. 2006-244264, while the master unit and the slave unit generate their own respective timing signals that are synchronized by correction of the phase difference thereof, because the timing signals are generated by way of respectively independent timing signal generation means, there may be a case where the cycle itself of the timing signals may differ. When the timing signal cycle differs, the actuated timing of the motors driven by the controllers deviates and a stable synchronous control cannot be produced.